Optimization of the USP assay for hyaluronidase.

The current USP XXII assay for hyaluronidase (EC 3.2.1.35, HAse) determines activity indirectly by measuring the amount of undegraded hyaluronic acid (HA) substrate remaining after the enzyme is allowed to react with the HA for 30 min at 37 degrees C. To be acceptable as a substrate, the HA must pass a USP suitability test. In this study, seven HA samples, which differed in their anatomical origin, their commercial supplier, and their chondroitin sulphate content, were tested as substrates. One of these did not pass the USP suitability test and therefore would not be an officially acceptable substrate; however, it was carried through the investigation along with the others in order to demonstrate its effect on the analysis. All seven HAs were used as substrates to assay testicular hyaluronidases from three different suppliers. The standard by which the other hyaluronidase activities were measured was USP hyaluronidase reference standard. The activity values calculated for a particular hyaluronidase differed significantly depending on which HA was used as substrate in its assay. Optimal results, as judged on the bases of initial purity, suitability for the assay, linearity of the standard curve, and per cent relative standard deviation of the measured activity, were obtained with a HA substrate derived from vitreous humour.